Temperature responsive control



y 6, 1958 v. WEBER ETAL 2,833,894

TEMPERATURE RESPCNSIVE CONTROL Original Filed Sept. 8, 1954 I 4Sheets-Sheet 1 INVENTORS 'VL'co Weber, Hag/2 1 @161" and J. HasseJLTHEIR ATTORNEY May 6, 1958' v. WEBER ETAL 2,333,894v I TEMPERATURERESPONSIVE CONTROL Original Filed Sept. 8, 1954 4 Sheets-Sheet 2INVENTORS V6660! Wefiel; Eng/'2 J FyZeP -a12d i Vcllc'alzz J Russell.

inf/W y 1958 v. WEBER srm. 2,833,94

TEMPERATURE RESPONSIVE CONTROL v Original Fil'ed Sept. 8, 1954 4Sheets-Sheet 3 INVENTORS V5660! ubez, Hagb J Tyler and William Jfiassedd.

' THE/H 14 7 TOR/VEY y 6, 1958 v. WEBER ETAL 2,833,894 TEMPERATURERESPQNSIVE comm.

Original Filed Sept. 8, 1954 4 Sheets-Sheet 4 Fig. 4.

INVENTORS' T i'cor' Vlbef, Hag b J Fgdef and Mllcanz J 36658868.

THE'IH I 141 2 ORNE' Y United States Robertshaw-Fulton Controls Company,Greensburg, Pa., a corporation of Delaware Original applicationSeptember 8, .1954, Serial --No. 454,753.; Divided and this applicationDecember 12; 1956, Serial N 0.. 627,908

7 Claims. (c1. zon -140 This application is a division ofourapplicationv Serial No. ,,454,753, filedSeptember 8, 1954. Thisinvention relates to thermostatic control devices and more par ticularly to an improved device which is particularly adapted forcontrolling a surface heating element of an electric range. I

Many foods require rapid initialheating to bring the food to apredetermined temperature and thereafter require. a reduced amount ofheat input to maintain such predetermined temperature. It .is an objectof this-invention to effect such a cooking operation by Permitting theheating element to operate at full energ'yinput until the temperature ofthefood .to be cooked reaches a pre; determined value, and then reducingthe energy .input to the heating element to maintain the food at theproper temperature. I p v Another object of this invention is toincorporate in a thermostatic control device a switching mechanism forreducing the energy input to a heating element as the controltemperature is approached during an increase in temperature.

Another object of the invention is to open a first pair of contacts of athermostatically operated switch at a first temperature condition and asecond pair of contacts at a second temperature condition. Anotherobject .of this invention is to enable manual selection of portions of aheating .element to obtaindifierent heating rates at different cookingtemperatures. 7

In one embodiment of the invention, switchingmechanism is; provided forperiodically making and. breaking the circuit to the heating element anda thermostatically operated switch controls ashunt .circuit which, whenclosed, supplies uninterrupted power to the heating element. t Openingof the thermostatically controlled switch at a predetermined temperatureof. the cooking vessel places the supply of power to the heating elementunder the control of the periodic cycling, mechanism. The amount ofenergy'supplied to the heating element will then be determined by thelength of the on period in each cycle. An additional thermostatic switchis pro vided for disconnecting the heater from the power source upon anexcessive temperature rise at the cooking vessel. The temperatureresponsive means is adjustable to effect switching from the continuousenergization arrangement to period energization' arrangement and tocomplete deenergization at selected temperatures. I I Other objects andadvantages will become apparent from the following description taken inconnection with the accompanying drawings wherein:

Fig. 1 is a schematic view of a surface heater of an electric range anda control device embodying this in vention;

Fig.2 is a view similar to Fig. 1 but showing a modi fied 'form of theinvention; b

Fig. 3 is 'a view similar'to Fig. l but showing another modified form ofthe invention; and

Fig. 4'is a view similar to Fig. 1 butshowing another modified form ofthe invention.

ice

. Referring more particularly to Fig. 1 of the drawings, there is shownan annular surface heating element 10 which is adapted to be supportedon the top plate of an electric range (not shown) in a manner well knownin the art. The heating element 10 is adapted to support a cookingvessel 12 thereon and is provided with a temperature sensing bulb 14which is located centrally thereof. 7

The bulb14takes the form of a flat hollow container whieh communicateswith a capillary tube 16 and is biased toward the cooking vessel 12 by aspring 18 seated on a suitable stirrup 20. The particular structure ofthe bulb 14 and mounting therefor-is fully disclosed and claimed inounce-pending application Serial No. 454,754, filed September 8, 1954,which is now Patent No. 2,786,930. I

.The capillary tube 16 also communicates with an eXpansible powerelement 22 which may consist of a pair of flexible diaphragms weldedtogether at their periphery and carrying a thrust button 24 on one sidethereof. The other side of the power element 22 is secured to a stud 26which is threaded through a suitable aperture 28 formed in a wall of acasing 30 to mount the power element 22 within a chamber 32 formed inthe, casing 30.

.Qne end of the stud 26 projects out of the casing 30 and carries amanually operable knob or dial 34 which maybe manipulated to rotate thestud 26 and thus effect axial adjustment of the power element 22relative to the casing, 30. t p

The assembly of the bulbv 14, capillary tube 16, and expansible powerelement 22 is filled with a suitable thermalfiuid which will expand uponincrease in temperature sensed by the bulb 14 to effect expansion of thepower element 22. v

.Disposed within the chamber 32 is a pair of spaced superposed fiiredcontacts 36, 38 which are engageable respectively by a pair ofmovable-contacts 40, 42. The movable contact 40 is carried on the freeend of a switch arm 44 which is pivoted at its other end 46 on thecasing 30, The switcharrn 44 underlies the thrust button 24 of the powerelement 22 and carries a block of insulating material 48 which isengageable by the button 24. .A spring 50 acts between the arm 44 andthecasirig.30 to bias the switch arm 44 in a clockwise direction, as.viewed in the drawing and thus bias the movable contact 40 toward thestationary contact 36.

The movable contact 42 is carried on one end of a switch.arm..52 whichunderlies. the switch ..arm,44 and is pivoted at its other end 54 on thecasing 30. A spring 56 acting between the casing 30 and the switch arm52 serves. to bias the latter in a clockwise direction and thus bias themovable contact 42 toward the stationary contact 38.

Abutment means is provided for transmitting movement from the switc harm 44 to the switch arm 52 for a purpose which will more fully appearhereinafter. This means takes the form of a screw 58 threaded throughthe switch arm 52 and extending toward the switch arm 44 tobe engageableby the block 48 carried by the switch arin 44. A v a The dial 34 isprovided with suitable cam me'ans 60 which 'co'a'ct with a normallyclosed switch 62 to open the same i'na selected position of the dial 34and thereby establish an on position for the control.

The range embodying this invention also includes cyclic switch meansindicated generally by the reference numeral 63 and including means forperiodically making and breakinga control circuit. The cyclicswitchmeans 63 is here shown "as c'omprising a hollow casing 64 having apair of fixed contacts 66, '68 mounted therein. The

fixed contacts 66, 68 are positioned to be connected by a contact bridge70 carried on a block of insulating material 72 which is secured to oneend of a bimetallic strip 74. The other end of the bimetallic strip 74is securely anchored to the casing 64. The bimetal strip 74 ispositioned in the casing 64 to hold the contact bar 70 in engagementwith the contacts 66, 68 when it is in its unheated condition. However,heating of the bimetal strip 74 will cause the same to flex and move thecontact bar 70 out of engagement with the contacts 66, 68.

Means are provided for alternately heating and cooling the bimetal strip74. This means is here shown as a heating coil 76 positioned within thecasing 64 beneath the bimetal strip 74 and connected at one end to thecontact bridge 70. The other end of the heater 76 is connected to asuitable terminal 78 which extends out of the casing 64.

Y The electrical connections between the various parts of the controlsystem will be brought out in a description of the operation of theapparatus which now follows.

As shown, the apparatus is in the off position with no electrical energybeing supplied to the surface heating element or the heating coil 76. Toplace the apparatus in operation, the dial 34 is rotated to a desiredtemperature setting. Such rotation of the dial 34 will move the cammeans 60 out of engagement with the switch 62 and permit the latter toclose. The temperature setting movement of the dial 34 will also serveto screw the stud 26 out of the casing 30 and move the power element 22upward, thereby permitting the movable contacts 40, 42 to move intoengagement with the fixed contacts 36, 38 respectively.

The apparatus is thus conditioned to supply a steady flow of electricalenergy to the surface heating element 10 through a circuit which may betraced as follows: line wire L1 of a suitable three-wire power source,wire 80, switch 62, wire 82, heating element 10, wire 84,-

wire 86, contacts 36, 40, switch arm 44, wire 88, wire 90, switch arm52, contacts 42, 38 and wire 92 to line wire L2.

When power is so supplied to the heating element 10, heat will begenerated thereby to raise the temperature of the cooking vessel 12 andthe food contained therein.

At this point, a circuit is also completed through the heating coil 76of the c clic switch means 63. This circuit may be traced as follows:line wire L2, wire 92, contacts 38, 42, switch arm 52, wire 90, wire 88,contact 68, contact bridge 70, heating coil 76, terminal 78, and wire 94to neutral wire N of the three-wire power source. Thus a voltage isimpressed across the heating coil 76 causing current to flow therein andraise the temperature thereof. The temperature increase of the heatingcoil 76 causes the bimetal strip 74 to become heated and to flex therebymoving the contact bridge 70 out of engagement with the contact 68 andbreaking the above traced energizing circuit for the heating coil 76.The heating coil 76 will then cool and permit the bimetal strip 74 tocool and return the contact bar 70 into engagement with the contacts 66,68. Movement of the contact bar into engagement with the contact 68again completes the energizing circuit for the heating coil 76 and thecycle of the cyclic switch means 63 is repeated.

When the contact bar 70 of the cyclic switch means 63 is in engagementwith the fixed contacts 66, 68, it also serves to complete an energizingcircuit for the surface heating element 10 which may be traced asfollows: line wire L1, wire 80, switch 62, wire 82, surfaceheatingelement 1%, wire 84, contact 66, contact bridge 70, contact 68, wire 88,wire 90, switch arm 52, contacts 38, 42 and wire 92 to line wire L2.

It will be apparent that the above traced energizing circuits for thetop heater 10 locate the switch 36, 40, 44 in parallel circuit with thecyclic switch 66, 68, 70 so that the former effectively shunts thelatter when it is in its closed position with the contacts 36, 40 inengagement with each other. Thus, as long as the contacts 36, 40

of the cyclic switch means 63 will not affect the steady energization ofthe surface heating element 10.

As the temperature of the cooking vessel 12 rises, the temperature ofthe bulb 14 will increase to cause expansion of the power element 22.Expansion of the power element 22 will move the thrust button 24 intoengagement with the block 48 to swing the switch arm 44 in acounterclockwise direction against the bias of the spring 50 and therebymove the contact 40 out of engagement with the fixed contact 36.

Opening of the contacts 36, 40 will break the circuit which shunts thecyclic switch 66, 68, so that current through the surface heater 10 mustflow through the switch 66, 68, 70. At this stage of the operation, thecontact bridge 70 is moving periodically into and out of engagement withthe contacts 66, 68 by the bimetal strip 74 and the heating coil 76.Accordingly, power is supplied to the surface heating element 10intermittently and the total amount of electrical energy supplied to thesurface heating element 10 will be determined by the cyclingcharacteristics of the switch means 63. It has been found that excellentresults are obtained if the cyclic switch means 63 is constructed toclose the energizing circuit for the surface heater 10 for approximatelyten seconds and maintain this circuit open for twenty seconds during athirty second cycle of the switch means 63. It will be understood,however, that other proportions of on and off time may be used.

When the switch 36, 40 is open and power is being supplied to thesurface heating element 10 under the control of the cyclic switch means63, the average rate of energy input to the heating element 10 issubstantially less than the steady input which occurs when the switch36, 40 is closed. Thus, the heat produced by the heating element 10 andtransmitted to the cooking vessel 12 is also reduced. Heat supplied tothe cooking vessel 12 at this reduced rate continues to raise thetemperature of the food therein, bringing it up to the desiredtemperature gradually.

It will be apparent that, since the thermal fluid within the bulb 14 isseparated from the vessel 12 by layers of metal and air, the temperaturethereof will necessarily lag behind the temperature of the vessel as thelatter rises. However, when heat is being supplied to the vessel at arelatively low rate, the degree at which the temperature of the thermalfluid lags the temperature of the food will be substantially less thanwhen heat is being supplied to the vessel 12 at a relatively high rate.Accordingly, reduction of the rate of heat input to the vessel 12 as thesame approaches the desired temperature, will reduce the possibility ofovershooting and consequent burning of the contents of the vessel 12. i

As the temperature of the vessel 12 rises as a result of theintermittent energy input to the heating element 10 under the control ofthe cyclic switch means 63, the temperature rise is sensed by the bulb14 and the power element 22 continues to expand. The continued expansionof the power element 22 moves the block 48 into engagement with thescrew 58 carried on the switch arm 52. Further expansion of the powerelement 22 imparts movement to the screw 58 to move the switch arm 52against the bias of the spring 56 and separate contacts 42, 38.

Opening of the contacts 38, 42 will break the intermittent energizingcircuit for the heating element 10 to further reduce the supply of heatto the vessel 12.

It is to be noted that after the steady and intermittent energizingcircuits for the heating element 10 are broken, the heating coil 76 isenergized from L1, wire 80, switch 62, wire 82, heater 10, wire 84,contact 66, contact bar 70, heater 76, and wire 94 to neutral wire N.Thus, the cyclic switch means 63 continues to cycle and is conditionedto take over the control of the energization of the heating element 10at any time. This is particularly important since initiation of cyclingin the cyclic switch means 63 may produce an initial cycle on the orderof operating temperatures. Preferably, the resistance of the heatingcoil- 76 is relatively high to hold the current flowing in the lasttraced circuit to a minimum.

As the temperature of the vessel 12, as sensed by the bulb 14, drops,the power element 22 willcontract to permit theswitch arms 44, 52 tomove upward under the bias of the springs 50, 56. This movement of theswitch arms 44, 52 will move the contact 42 into engagement with thecontact 38 to once again complete the intermittent energizing circuitfor the-heating element and restore the relatively low rate of heatsupply to the vessel 12. Usually, the restoration of the reduced rate ofheat input will serve to restore the desired temperature to the vessel12 to again cause expansion of the power element 22 and openingof thecontacts 38, 42. However, in the eventthat the reduced heat input is notsufiicient to restore the desired temperature, the power element 22 maycontract sufiiciently to close the contacts 36,40 thereby completing:the circuit which shunts the cyclic switch means, 63 and provides acontinuous supplyofelectric energy to the heating element 10.

It. will beapparent from the foregoing that the apparatus shown in Fig.l is operative to bring the temperature of a cooking vessel rapidly upto a temperature ap-' preaching the desired control temperature bysupplying power continuously to the heating element 10 and thereaftereiiecting a gradual temperature rise of the cooking vessel 12 totheselected cooking temperature by supplying powerintermittently to theheating element 10;. sub? sequent maintenance of theselected'temperature of the cooking vessel 12 being efiected'bysupplying intermittent or continuous power to the heating. element 10'in re sponse to temperature variations of the cooking vessel 12. Thetemperature at which the power supply to, theheating element 10 isswitched from continuous'to intermittent is accurately determined withrespectto the. de siredtemperature of the cooking vessel 12, asselectedby the setting of the dial 3 4, by means of the screw 58. carried onytheswitch arm 52. The screw 58 may bethreaded into the switcharrn 52 toadjust the differential between the temperatures at which the switcharms 44,- 52 will. open'their respective contacts. Thus, thescrew 58effectively adjusts the temperature span in which the cyclic switchmeans 63 will control the cookingoperation.

Fig.2, wherein parts corresponding to parts hereinbefore described aregiven like reference'numerals. This embodiment is similar to theembodiment shown in Fig.1 but differs therefrom in the formandelectrical hookup of the cyclic switch means.

The cyclic switch means 63 of Fig. 2' comprises a casing 64 having afixed'contact 68 mounted therein. A;

bimetallic switch arm 96 is secured at one endto the casing 64 andcarries on its other end a movable contact 98 which is engageable withthe fixed contact 68. A heat ing coil 100 encircles the bimetallicswitch arm 96 and is connected at one end to the movable contact98: Theother end of the heating coil 100 is connected to the wire 84 which inturn is connected tothe surface heating ele-' ment 10 and to the fixedcontact 36 of the thermostaticswitch.

In the normal or unheated condition of the bimetallic switch arm 96,thecontact 98-is in engagement with the fixed contact 68 so that theheating coil 100 is connected:

Another embodiment of the invention isshown-inwire 84,heating"coi-l.100, contacts 98, 68, wire 88, switch arm 52,'contacts 42,38, and'wire 92 to line Wire L2.

Energization'of the heating coilf results in-heating of the bimetallicswitch arm 96*and warping'of the same to move the contact'98 out ofengagement'with the contact 68. energizing circuit for the heating coil100- and permits the bimetallic switch arm 96- to cool and return thecontact 98 into engagement with the fixed contact 68; Closing of thecontacts 98, 68-Will again complete the energizing circuit for theheatingcoil-100 and the operating cycle of the switch means 63 willberepeated. Thus, the cyclic switch means 63 will continue to make andbreak as long as it isconnected to the source.

If desired, there may be inserted in the wire 86 a resistance 101 (shownin broken lines in Fig. 2) ofsufficient ohmic value relative to theresistance of the coil 100 to cause the coil 100 to draw enough currentto effect the above described cycling operation even when ;the contacts36, 40 of the thermostatic switch are'closed to establish a shuntcircuit across the heating coil 100.

When the resistance 101 is so used, cycling of the switch in that theenergizing circuit for the heating coil of thecyclic switch means 63 isbroken when the power element 1 22 expands sufficiently to open thecontacts 38, 42.

Another embodiment of the invention is illustrated in Fig. 3, whereinparts corresponding to parts hereinbetends between the bimetallicresistance element 102 and a movable switch arm 110. The switch armcarries a contact 112 which is engageable with the fixed-contact 68. Theswitch arm 110 is connected to the wire 84 and the fixed contact 68 isconnected to the wire 88 so that the contacts 112, 68 controlintermittent energization of the surface heater 10.

To eltect periodic opening and'closing of the contacts 112, 68, thebimetallic resistance element 102 is connected to the wire 82 by a wire114 and the fixed contact 106 is connected to the wire 84 which in turnis connected to the neutral wire N of the power source.

In the normal or unheated condition of the bimetallic resistance element102, the contact 104 is in engagement with the fixed contact 106 so thatthe bimetallic resistance element 102 is connected directly between linewire L1 and neutral wire N by a'circuit which may be traced as follows:line wire L1, Wire 80, switch 62, wire 82, wire 114, bimetallicresistance element 102, contacts 104, 106, I

breaking the energizing circuit for the bimetallic resistance elementand permitting the same to cool. Cooling of the bimetallic resistanceelement 102 will cause the same to return to its initial position'andmove the contact" Opening of the contacts 98; 68 breaks the 104 intoengagement with the contact 106. Closing of the contacts 104, 106 willagain complete the energizing circuit for the bimetallic resistanceelement 102 and the operating cycle of the switch means 63 will berepeated. Thus, the cyclic switch means 63 will continue to make andbreak as long as the switch 62 is closed.

The pin 108 establishes a mechanical connection between the bimetallicresistance element 102 and the switch arm 110 so that making andbreaking of the contacts 104 with associated movement of the bimetallicresistance element 102 will cause corresponding making and breaking ofthe contacts 112, 68 in the energizing circuit for the surface heater10.

Operation of the apparatus shown in Fig. 3 is similar to the operationof that shown in Fig. 1, differing only in that the energizing circuitfor the bimetallic resistance element is connected directly across thesource at all times and current flowing therein is at no time requiredto flow through the surface heater 10.

Another embodiment of the invention as illustrated in Fig. 4 whereinparts corresponding to parts hereinbefore described are designated bycorresponding reference numerals. This embodiment is similar to theembodiment shown in Fig. 1 but differs therefrom in the form of thesurface heater and also in the form of the manually operable switchwhich connects the surface heater directly to the power source.

The surface heater of Fig. 4 takes the form of two heating elements.116, 118 connected in parallel between the wire 84 and the line wire L1of the three-wire power source. Connected in series with the heatingelement 118 is a first manually operable switch means comprising a fixedcontact 120 and a movable contact 122 which is carried on the switch arm124. The switch arm 124 is pivoted in the casing 30 and is connected tothe line wire L1. A spring 126 acting between the switch arm 124 and thecasing 30 biases the switch arm 124 in a direction to normally hold thecontact 122 in engagement with the contact 120.

Connected in series with the heating element 116 is manually operableswitch means comprising a fixed contact 128 mounted on the casing 30 tobe engageable by a movable contact 130. The contact 130 is carried on aswitch arm 132 pivoted on the casing 30 beneath the switch arm 124. Theswitch arm 132 is connected to the line wire L1 and is biased by aspring 134 to normally hold the contact 130 in engagement with thecontact 128. A screw 136 is threaded through the switch arm 132 andabuts the switch arm 124- for a purpose which will more fully appearhereinafter.

Manually operable means is provided for moving the contacts 122, 130 outof engagement with the contacts 120, 128, respectively when the dial 34is moved to a predetermined position to provide an off position for thecontrol wherein the heating elements 116, 118 will be disconnected fromthe power source. To this end, a cam 138 is formed on the underside ofthe dial 34 to be engageable with one end of a push rod 140. The pushrod 140 is slidably mounted in the casing 38 and the other end thereofextends into engagement with the switch arm 124. The push rod 140 is ofsufiicient length to hold the contact 122 out of engagement with thecontact 120 when the outer end of the rod 140 is in engagement with thecam 138. Rotation of the dial 34 to move the cam 138 out of engagementwith the push rod 148 will permit the switch arm 124 to move under thebias of the spring 126 to position the contact 122 in engagement withthe contact 120. Since the screw 136 carried by the switch arm 132 abutsthe switch arm 124, the switch arm 132 will follow the movements of theswitch arm 124 so that the cam 138 and push rod 140' also serve tooperate the contacts 128, 130.

Operation of the apparatus in Fig. 4 thus far described is similar tothe operation of that shown in Fig. 1 with the contacts 120, 122, 128,performing the same function as the switch 62 of Fig. 1 and the parallelconnected heating element 116, 118 operating in the same manner as thesurface heater 10 of Fig. 1. However, if a relatively small mass of foodis to be cooked in the vessel 12, it may be desirable to utilize onlyone of the heating elements 116, 118. Accordingly, manually operablemeans are provided for latching the contacts 128, 130 in open positionto disconnect the heating element 116 from the power source.

This means takes the form of a bell crank lever 142 pivoted in thecasing 30 with one leg thereof extending into engagement with the switcharm 132. The other leg of the bell crank lever 142 extends upward and isprovided with a suitable seating surface 144 which is engageable by aplunger 146. The plunger 146 is slidably mounted in the casing 30 withone end thereof projecting out of the casing and carrying a push button148.

The plunger 146 is biased away from bell crank lever 142 by a spring 150acting between the casing 30 and a collar 152 formed on the plunger 146.The collar 152 is engageable with the wall in the casing 30 to form alimit stop and prevent ejection of the plunger 146 from the casing.

The spring 150 normally holds the plunger 146' out of engagement withthe bell crank lever 142 so that the contacts 120, 122', 128, 130 willoperate solely under control of the cam 138 and push rod 140. However,when the plunger 146 is moved downward against the bias of the spring150 by manipulation of the push button 148, the inner end of the plunger146 engages the seating surface 144 on the bell crank lever 142,pivoting the bell crank lever 142 and imparting counterclockwisemovement to the switch arm 132. This movement of the switch arm 132moves the contact 130 out of engagement with the contact 128 anddisconnects the heating element 116 from the line wire L1.

To maintain the heating element 116 in its inoperative condition,latching means is provided for holding the plunger 146 in its depressedposition to maintain the contacts 128, 130 out of engagement with eachother. To this end, a hook latch 154 is pivoted on the casing 30adjacent the push button 148. The hook latch 154 is adapted to be hookedover the top of the push button 148 when the same is depressed to retainit in its depressed position until the hook latch 154 is manuallyreleased.

In operation, rotation of the dial 34 to move the cam 138 out ofengagement with the push rod 140 would permit the switch arms 124, 132to move in a clockwise direction under the bias of the springs 126, 134and close contacts 128, 122, 128, 130. The heat ing element 116 is thenconnected between wire 84 and line wire L1 through a circuit which maybe traced as follows: line wire L1, switch arm 132, contacts 130, 128,wire 156, and heating element 116 to wire 84.

The heating element 118 is connected between line wire L1 and wire 84through a circuit which may be traced as follows: line wire L1, switcharm 124, contacts 122, 120, wire 158, heating element 118, and wire towire 84.

It will be apparent from the foregoing that the operation of theapparatus of Fig. 4 is similar to that of Fig. 1 difiering only in thatportions of the surface heater may be manually selected for use in theheating operation.

While four embodiments of the invention have been herein shown anddescribed, it will be obvious to those skilled in the art that theinvention may be variously embodied and that changes may be made in theconstruction and arrangement of parts without departing from the scopeof the invention as defined in the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A thermostatic control device comprising a casing,

a pair of fixed contacts mounted on said casingin spaced superposedrelation, a pair of movable contacts mounted in said casing in spacedsuperposed relation and being cooperable with said fixed contactsrespectively for controlling a heating circuit, means for biasing saidmovable contacts into engagement with said fixed contacts, thermallyresponsive means including an expansible element mounted on said casingand being operatively engageable with one of said movable contacts formoving the same out of engagement with one of said fixed contacts upon apredetermined expansion of said element, and abutment means threadedlymounted on the other of said movable contacts to extend laterally towardsaid one movable contact and being operatively engageable by said onemovable contact for moving said other movable contact out of engagementwith the other of said fixed contacts upon a further expansion of saidelement.

2. A thermostatic control device comprising a casing, 21 pair of fixedcontacts mounted on said casing in spaced superposed relation, a pair ofmovable switch arms mounted in said casing in spaced superposedrelation, each of said switch arms having a contact movable therewithand being biased to normally hold said movable contacts in engagementwith said fixed con tacts respectively, thermally responsive meansincluding an expansible element mounted on said casing and beingoperatively engageable with one of said switch arms upon expansionthereof for moving said one switch arm from its biased position, and anyadjustable abutment means mounted on the other of said switch arms between said switch arms for establishing an operative connectiontherebetween and moving the other of said switch arms from its biasedposition upon further expansion of said element.

3. A control device as claimed in claim 2 wherein said abutment meanscomprises a member threadedly carried on said other switch arm andextending toward said one switch arm, said member being adjustablelaterally of said one switch arm to vary the degree of said furtherexpansion required to actuate said second switch arm.

4. A thermostatic control device comprising a casing, a pair of fixedcontacts mounted on said casing in spaced superposed relation, a pair ofmovable contacts mounted in said casing in spaced superposed relationand being engageable with said fixed contacts respectively, temperatureresponsive means including a movable element in said casing operativelyconnected to one of said movable contacts for actuating the same,adjustable abutment means mounted on said one movable contact andextendinglaterally thereof for actuating the other of said movablecontacts, a second pair of fixed contacts mounted in said casing, asecond pair of movable contacts mounted in said casing and beingengageable with said second pair of fixed contacts respectively,adjusting means for said temperature responsive means, means operativelyassociated with said adjusting means for actuating said second pair ofmovable contacts, and manually operable means for actuating one of saidsecond pair of movable contacts.

5. A thermostatic control device as claimed in claim 4 wherein saidmanually operable means comprises an axially movable plunger extendingfrom said casing, and a latch member is provided for latching saidplunger in one position thereof.

6. A thermostatic control device for a parallel circuit having a sourceof electric energy comprising a casing, switch means mounted in saidcasing and having open and closed positions for controlling energizationof the parallel circuit, thermally responsive means including anexpansible element mounted on said casing and being operativelyassociated with said switch means for actuating the same between saidpositions, adjustment means for said temperature responsive meansincluding a rotatable member mounted on said casing in spaced superposedrelation, a plurality of fixed contacts mounted in said casing, aplurality of movable contacts mounted in said casing in spacedsuperposed relation and cooperable with said fixed contacts to connectportions of the parallel circuit to the source respectively, cam meansassociated with said rotatable member, and an operative connectionbetween said cam means and said movable contacts for actuating the sameto an open position upon rotation of said rotatable member to apredetermined position, said operative connection including anadjustable abutment means mounted on one of said movable contacts andengageable with the other of said movable contacts.

7. A thermostatic control device as claimed in claim 6 wherein manuallyoperable means are provided for actuating at least one of said movablecontacts independently to selectively energize at least one portion ofthe parallel circuit.

References Cited in the file of this patent UNITED STATES PATENTS2,385,434 Weber Sept. 25, 1945 2,403,824 Newell July 9, 1946 2,441,192Graves May 11, 1948 2,591,803 Garner Apr. 8, 1952 2,671,136 GreenawaltMar. 2, 1954 2,715,664 Garner et a1. Aug. 16, 1955 2,718,574 Weber etal. Sept. 20, 1955

